1. Field of the Invention
This invention relates to a push-pull output circuit using insulated-gate type field-effect transistors (IGFET or MISFET, referred to simply as FET, hereinbelow), and more particularly to a push-pull output circuit using both enhancement-type and depletion-type FET's disposed in a semiconductor substrate.
2. Description of the Prior Art
Many push-pull output circuits using FETs have been proposed for switching or digital circuits such as in a circuit for an electronic desk top calculator. Since such push-pull output circuits are generally formed as integrated circuits or large-scale integrated circuits on silicon chips together with the other digital circuits, low power consumption thereof is required. An example of a push-pull circuit comprises first and second inverters, each formed of an enhancement-type load FET and an enhancement-type driving FET. In such circuits, the utilization of the power supply voltage is low due to the built-in potential in respect of the substrate in the load FET, namely, the substrate bias applied to the substrate acting as a second gate of the FET. Recently, another type of push-pull FET output circuit has been proposed which utilizes depletion-type FETs as the load elements. But such a circuit is also accompanied with the drawback that the power consumption is large.